The management of large numbers of injured patients expected during catastrophic events - either from natural, unintended or deliberate incidents (e.g. 'all hazards events') could quickly overwhelm existing healthcare resources jeopardizing the lives of victims and healthcare providers. No consensus currently exists on standardized definitions or data needed for effective mass casualty triage. No outcome studies validate data needed for incidents involving chemical, radiological, or biological material, and none are appropriate for use with victims of all ages. Our broad long-term goal is to validate the accuracy of triage systems that are appropriate for use in chemical events with adult victims. We propose a study using health outcome data from a large chlorine leak to determine whether the data collected in four triage systems accurately predict actual clinical status. Six datasets collected from a chlorine leak that occurred in 2005 include patient demographics, exposure estimates, symptoms, outcome categories, and physiological measurements for more than 900 victims. Research studies published on these data indicate that oxygen saturation was predictive of acute medical outcomes. These data will be used to address the following specific aims: 1) Generate a research dataset useful for further analysis by linking actual data from six chlorine leak datasets to explore measures for completeness and robustness (to test RQ1). 2) Develop a statistical model using medical outcome categories and oxygen saturation levels as measures of medical outcome to compare four adult triage systems (to test RQ1). 3) Evaluate the ability of four adult triage systems to accurately predict medical outcomes using the statistical model (SA2) and research dataset (SA1). 4) Explore the development of a data driven model to triage patients using the research dataset (SA1) to predict medical outcomes for adults (to test RQ2). Research questions that frame the study: 1) What is the association between data collected in the four adult triage systems most frequently used in the U.S. and severity of respiratory signs/symptoms necessitating medical intervention from chlorine leak patient datasets? 2) What additional information in an adult mass casualty triage system sufficiently improves the prediction of an accurate triage classification for initial treatment that involves a chemical incident?